1. Field of the Invention
The present invention relates generally to a filtration device used to remove contaminants, typically particulate matter or moisture from air used to purge a vapor canister. More specifically, the filtration device causes the air entering the device to flow along the inner circumference of a cylinder thereby generating an air stream having a sufficient flow velocity such that centrifugal force forces the contaminants against the side walls of the filter case whereafter they fall out of the air stream and collect in a low velocity cavity or dead air space.
2. Description of the Related Art
Conventional motor vehicles, due to increased emission standards, typically include a fuel vapor recovery system. The fuel vapor recovery system includes a vapor or purge canister for receiving fuel vapors generated in the fuel tank. A fuel vapor absorbent, typically activated charcoal, located in the vapor canister retains the fuel vapor when the vapors are displaced from the fuel tank during refilling. During operation of the engine, the fuel vapor contained in the vapor canister is purged by drawing fresh air through the canister and into the intake manifold of the engine.
Some fuel vapor recovery systems include a filtration device to filter the fresh air introduced into the canister during the purge operation. Filters used in the past include a foam filter placed in a rectangular box. However, water tends to pass through the foam filter and into the canister which reduces the effectiveness of the absorbent or charcoal. Also, dust or other contaminants build up on the foam filter and clog the filter which further reduces its efficiency.
Thus, it is desirable to have a low cost, low maintenance filtration device that does not require a complex, self-cleaning apparatus to filter the fresh air supplied to the vapor recovery canister.
Accordingly, the present invention provides a filtration device for use with a fuel vapor recovery system of the type using a vapor storage canister. The filtration device includes a housing defining a chamber. The chamber includes an interior surface. Air enters the chamber through an inlet port formed on the interior surface of the chamber. Air entering the chamber swirls within the chamber in a circular or cyclonic motion whereby particulate matter or moisture of sufficient mass contained in the air is forced against the interior surface of the chamber. These particulates then fall downward along the interior surface and ultimately into a debris collection bin. During the purge process, clean air is drawn from the chamber through an outlet port positioned in the center of the chamber.
The filtration device may also include a secondary filter, such as a foam filter element, that further filters the purge air before it is drawn into the vapor canister. The particles fall into the debris collection bin or dead air space, which may include a top that reduces the likelihood that particulate material or moisture will splash upwardly and enter the outlet passage.